An electrophoretic display generally comprises a suspension of charged pigment particles collodially dispersed in a light transmissive liquid contained in a cell. In one embodiment, the cell comprises two parallel and transparent conducting electrode panels. The charged particles are moved between the electrode panels under the influence of an electric field. In an alternative embodiment the cell comprises transparent front window and rear panel and non obstructing collecting and counter electrodes. Charged particles are either dispersed throughout the cell or collected on the collecting electrode. Other embodiments of electrophoretic cells are known to those skilled in the art. During operation of an electrophoretic display, charged pigment particles are moved through the liquid under the influence of an electric field. During this movement, the pigment particles can become agglomerated which hinders effective operation of the cell.
In U.S. Pat. No. 4,285,801, Chiang discloses utilizing ionic fluorinated long chain organic molecules as dispersants for pigments. The molecules are absorbed onto the surface of the pigment particles by ionic interaction. Unfortunately, during operation of the cell the dispersant molecule can in the electric field become separated from the pigment particle causing destabilization of the pigment particle.
There is a continuing need to provide effective stabilization of charged pigment particles in electrophoretic displays to ensure that the particles are effectively suspended to minimize agglomeration.
It is therefore an object of the present invention to provide an improved electrophoretic display. Other objects and advantages will become apparent from the following disclosure.